Frequency shifter

[xmacex]

Hi. This thing is a lot of fun. There is a pitch shifter, but I wonder whether also a frequency shifter would be useful/interesting/weird? What's the difference? Doepfer explains

A frequency shifter is an audio processing unit that shifts each frequency of the incoming audio signal by the same frequency. If the shifting frequency is e.g. 200Hz an incoming audio frequency of 1000 Hz becomes 1200 Hz, 2000Hz becomes 2200 Hz, 3000 Hz becomes 3200 Hz and so on. Pay attention that this is different from pitch shifting where all frequencies are shifted proportional (e.g. 1000>1200Hz, 2000>2400Hz, 3000>3600Hz)!

SuperCollider has FreqShift, so I am attempting to have a go at this with my modest SuperCollider skills. Pedalboard seems to be well engineered, so I think I got a working version going in one and a half hours or so.

Would such a thing be of interest to be considered to be included in Pedalboard?

[xmacex]

It is working, and besides making silly sounds, I am having a bit of trouble tuning it.

There are very tasty phasing effects going on near 0, but frequency shifting at audio also seems to sounds pretty great. I am a little unsure if negative frequency shifting makes sense, but Doepfer A-126-2 seems to have both negative and positive directions. It has two controls, coarse ranging 20Hz-5kHz and fine. The earlier A-126 went from about 50kHz to 5kHz, and lower speeds available with patching.

My version only has one knob right now, it goes from arbitrary -333 Hz to 333 Hz. There are a lot of strange sounds in there, but the Pedalboard UI is a bit unwieldy for tuning into those very low values when it is linear, and I didn't yet figure out if the UI dials can be exponential in both directions. This would involve some math, as exponentials of negative numbers are not like negatives of positive numbers, like a parabolic or something. In the parameter menu one can use K3 to finetune, but it would of course be better if the script UI itself was useful.

So feedback on parameter tuning would be welcome. Here are some ideas I can think of

1. Wide bipolar range, say -333 to 333 Hz or even much more
2. Narrow bipolar range, say -10 to 10 Hz
3. Exponential unipolar range, say 0.001 to 5000 Hz
4. Parabolic bipolar range, say -5000 to 5000 Hz
5. Coarse and fine tune dials
6. Two separate pedals, one with narrow and one with wide range
7. Some other ideas

PS. I have (yet, will study) no idea how frequency shifting actually works, in acoustics, electronics or SuperCollider. The FreqShift of SuperCollider says it is

FreqShift implements single sideband amplitude modulation, also known as frequency shifting

Does "single sideband" mean that shifting both up and down makes no sense, and only shifting up would not miss out on anything? I will need to experiment with the examples SuperCollider provides.

My hope is that frequency shifting is, and sounds different enough to amplitude modulation that a one would be worthwhile to include in Pedalboard.

[xmacex]

I chose option number 5, with a coarse and a fine tune dial. There is an item in the roadmap about a system of simple and fine control but I did what the adjacent pitch shifter does, by implementing _message_engine_for_param_change(param_id, value).